In order to create the illusion of more than one guitar part, you first need to think about manipulating the stereo image. It may be obvious, but if you are doing this in a live environment, make sure your laptop is sending a stereo output to the PA or all of this is wasted!
Here, we've kept the piezo signal central and panned the individual strings incrementally across the stereo image from left to right with the following values: Low E string 100 percent left, A string 70 percent left, D string 40 percent left, G string 40 percent right, B string 70 percent right, high E string 100 percent right.
It's beginning to sound like two guitars already. Hear the extra separation in the following clip: